This disclosure relates in general to communication systems and to location-aware communication systems amongst other things.
Wireless handheld radios communicate with each other so long as there is sufficient signal to discern the received signal. Some handheld radios allow adjusting the sensitivity to received signals using a knob that is called a squelch. Received signals of lower power can be filtered out by the squelch. The squelch function is not tied to distance between handheld radios, but signal strength, which may not correlate well to the distance.
There are family radios (i.e., FRS or GMRS band radios) and wireless phones that include a global positioning system (GPS) receiver. These devices can both communicate and determine location. The location and communication functions are often not tightly coupled in most circumstances. Some family radios with GPS allow communicating locations of radios to other radios nearby. During emergency phone calls, the location of the wireless phone can be identified and relayed to emergency responders to allow responders to locate the caller.
Limiting communication between first responders to emergencies allows efficient communication without interference. A squelch feature can limit analog communication to those signals that are strong from those that are weaker, which may not limit communication precise enough. Consider an example where emergency responders in a tall building use a squelch feature to try to limit communication to those in the building. When near the windows, strong signals will be received from far away given little obstruction, but another responder two floors down may have a very weak signal. Adjusting the squelch will filter those a few floors away, but not someone in line of sight miles away.